The present invention relates to a method and apparatus for treating medical implements waste involving used hemodialyzers, used syringes, used injection needles, used gauze, used vessels and so on.
In order to prevent infectious medical wastes discharged from hospitals, dialysis facilities and the like from causing secondary infection, a guideline for specifying the method of treating such wastes was published by the Welfare Ministry of Japan on Nov. 7, 1989 and enforced on Apr. 1, 1990. This guideline imposes duty on hospitals, dialysis facilities and the like to sterilize the medical implements waste discharged therefrom, as a general rule.
Japanese Patent Unexamined Publication No. 1-176486 discloses a treatment method and apparatus in which used synthetic resin syringes and injection needles are contained in a heat-resistant container, heated and melted at a predetermined temperature for sterilization and then cooled for solidification.
Japanese Utility Model Unexamined Publication No. 1-144040 discloses an apparatus for heat-sterilizing wastes in which wastes are heat-sterilized and then crushed by a crusher for reducing the volume.
Japanese Patent Examined Publication No. 51-25470 discloses an apparatus for treating plastic wastes in which plastic wastes are placed in a cylinder, heated by a heater contained in the bottom plate of the cylinder and a piston and compressed, and, at the same time, integrally molded by mainly melting the surfaces.
Japanese Patent Unexamined Publication No. 1-315383 discloses an apparatus in which used disposable syringes are heat-sterilized by an electric heater and a far infrared heater, both of which are provided in the side and bottom surfaces of a heating furnace. A method is also disclosed as an embodiment in which wastes to be treated are melted in a heat-resistant container, cooled and then discharged as one product containing needles.
Japanese Patent Unexamined Publication No. 1-263410 discloses an apparatus for heating wastes by microwaves, and drying, burning and then ashing the wastes.
When wastes such as hemodialyzers and the like, which are made of plastics having different melting points, are treated by using the treatment method and apparatus disclosed in Japanese Patent Unexamined Publication No. 1-176486, volume reduction (molding) is insufficiently effected because many wastes remain unmelted at the treatment temperature. When wastes containing polyvinyl chloride are treated, since HCl gas is generated at 190.degree. C. or more, off-gas treatment is required.
In addition, the method of crushing by a crusher in the apparatus for heat-sterilizing wastes disclosed in Japanese Utility Model Unexamined Publication No. 1-144040 has the disadvantages that the effect of reducing the volume of wastes is not always excellent, and that there are needs for the maintenance of the crusher cutter and for many power sources generating great noise and vibration.
The apparatus for treating plastic wastes disclosed in Japanese Patent Examined Publication No. 51-25470 has the disadvantage that, since the apparatus is proposed on the basis of the idea that only the surfaces of wastes are coated with a melt, without the intention of sterilizing the wastes, the molded product has poor stability.
The apparatus disclosed in Japanese Patent Unexamined Publication No. 1-315383 has the disadvantage that, since large wastes to be treated such as used hemodialyzers, which contain water, cannot be easily heated only by circulating hot air, the wastes are insufficiently sterilized, and much time is required for treatment. In addition, because a hemodialyzer is made of various kinds of plastics, melted and unmelted portions are mixed at a certain treatment temperature, and thus a reduction in volume cannot be sufficiently effected.
Further, when wastes to be treated such as used hemodialyzers, tubes and the like, which are made of various kinds of plastics, are treated by the apparatus disclosed in Japanese Patent Unexamined Publication No. 1-263410, since toxic gas such as hydrogen chloride or the like is generated, it is necessary to take into account the material for the apparatus and the treatment of the exhaust gas, resulting in the complication of the apparatus. There are also the disadvantages that the method of reducing the volume by ashing using microwaves requires much power, and the apparatus itself is heated to a high temperature and is thus unsuitable for installation in hospitals and clinics.
On the other hand, medical waste products contain various kinds of plastics. For example, when the ratios of the raw materials which form a hemodialyzer set including a blood circuit (tube and the like), a syringe, a physiologic saline container and so on were measured by analysis, the following results were obtained:
______________________________________ (1) Polyvinyl chloride 50% by weight (2) Polystyrene or polycarbonate 30% by weight (3) Cellulose or synthetic film 5% by weight (4) Polyethylene, polypropylene 5% by weight or silicone (5) Polyurethane and stainless 10% by weight steel ______________________________________
The properties of main plastics of the above materials are given in Table 1.
TABLE 1 ______________________________________ Material Melting Softening Name Point Point Note ______________________________________ Polyvinyl about 65-85.degree. C. HCl gas is generat- chloride 170.degree. C. ed at 190.degree. C. or more. Polystyrene about 90-102.degree. C. Deformation temp- 230.degree. C. erature; 70-100.degree. C. (ASTM D648) Softening point; 97-100.degree. C. (ASTM D1525-58T) Polycarbonate about 145-165.degree. C. Deformation temp- 230.degree. C. erature -260.degree. C. (ASTM D648) 130-136.degree. C. (18.6 kg/cm.sup.2) 136-142.degree. C. (4.6 kg/cm.sup.2) (Medium- about Softening point; density) 120.degree. C. 100-120.degree. C. Polyethylene (ASTM D1525) Deformation temp- erature; 50-66.degree. C. (ASTM D648) Polypropylene about 96-105.degree. C. 180.degree. C. (ASTM D1525) ______________________________________ Remarks: ASTM (American Society for Testing and Materials)
In addition, a relation between the heating temperature and the gases generated were examined for a polyvinyl chloride tube (blood circuit) by the method below. A glass bottle having an internal volume of 1 l and a heat insulator provided at the bottom was disposed in an intermediate portion in a drying furnace having an electric heater provided at the inner bottom thereof. A blood circuit (main component: polyvinyl chloride) was placed in the glass bottle and sealed by a stopper. A thermometer and a sampling tube were passed through the stopper so that the temperature at the inner bottom of the glass bottle and the concentrations of the gases generated were examined. The results obtained are shown in Table 2. The hydrogen chloride gas generated was detected by using detector tubes with measurement ranges of 1 to 20 ppm and 20 to 500 ppm, and the carbon monoxide gas generated was detected by using a detector tube with a measurement range of 25 to 500 ppm.
TABLE 2 ______________________________________ Temperature Concentration of gas generated [.degree.C.] HCl [ppm] CO [ppm] ______________________________________ 165 2 60 170 2 50 175 2 60 180 3 120 185 200 500 or more 190 500 or more ______________________________________